The pisiform bone (also called pisiforme or lentiform bone) is a small knobbly, pea-shaped wrist bone. It forms the ulnar border of the carpal tunnel. It is spheroidal, although it can be quite variable in shape. It sits on a plane palmar to all the other carpal bones. The pisiform bone is found in the proximal row of the carpus. It is located where the ulna (inner bone of the forearm when in anatomical position) joins the carpus (wrist). It articulates only with the triquetral. It is a sesamoid bone. The pisiform bone may be known by its small size, and by its presenting a single articular facet. It is situated on a plane anterior to the other carpal bones and is spheroidal in form. Surfaces Its dorsal surface presents a smooth, oval facet, for articulation with the triquetral: this facet approaches the superior, but not the inferior border of the bone. The palmar surface is rounded and rough, and gives attachment to the transverse carpal ligament, and to the Flexor carpi ulnaris and Abductor digiti quinti. The pisiform bone is palpable on the palmar surface about three centimeters distal to the head of the ulna. The lateral and medial surfaces are also rough, the former being concave, the latter usually convex. The lateral surface is usually marked by a shallow groove for the ulnar artery.